Although great strides have been made toward development of safer, more individualized therapies for breast cancer, many new treatments that exhibit potential efficacy against 2D cancer cell lines fail to show therapeutic value when tested in vivo. Thus, 3D models that more accurately reflect in vivo physiology are necessary to streamline drug development. In this proposal, we will create a 3D bioprinted model of human breast cancer that incorporates a focus of cancer cells surrounded by an architecturally-defined stromal compartment composed of human fibroblasts, endothelial cells, and adipocytes. Tissue model design targets include generation of well-defined cancer and stromal compartments, persistent and proliferative tumor cell nodules, well-organized microvasculature, lipid accumulation in adipocytes, and native-like extracellular matrix deposition. Once the model is established reproducibly, 3D bioprinted tissues or matched 2D cell lines will be treated with chemotherapeutic agents from the NCI Developmental Therapeutics Program Approved Oncology Drugs Set to determine the relative efficacy of treatments in 2D versus 3D. The proposed model is versatile and allows for incorporation of many cell types from primary, patient-derived, and commercial sources to provide a flexible in vitro screening platform with which in vivo drug responses can be predicted more accurately.